In certain solenoid operated fuel injectors the armature is disposed in the internal fuel path through the fuel injector, and the valve element joined to it so that the two form a unitary subassembly. Since the armature forms part of the magnetic circuit, its design must take into account both magnetic circuit and fuel flow restriction considerations, among others. On the other hand, the valve element design must, among various considerations, including fuel flow restriction, also take in account sealing against a hardened valve seat which it repeatedly impacts during operation. Hence the armature and valve element are typically different materials, the former being a relatively magnetically soft, ferromagnetic material and the latter a relatively magnetically hard ferromagnetic material. In efforts to minimize restriction that an armature imposes on fuel flow, armatures have heretofore been designed with internal passages that allow fuel to flow through them and/or external flats or channels that provide greater flow area around the exterior of the armature.
Flow passages in an armature are commonly in the vicinity of the armature to valve element attachment interface. Crimping and/or welding are two processes that have been used to join the valve element to the armature, and they require that certain minimum amounts of material be available at the attachment interface so that the attachment can be successfully accomplished. This tends to compromise the amount of material that can be omitted in order to improve the fuel flow past and/or through the armature. Consequently, prior armature designs employed a number of small holes through the bottom and/or flats or channels on the outside diameter. Such solutions may require multiple machining operations and/or may still not achieve the necessary reduction in restriction that is required to handle relative high flow rates.
The present invention relates to an improved solution that resides in a construction for the armature that is believed to be entirely novel, both per se and in combination with certain associated parts of a fuel injector. The invention still allows crimping and/or welding to be used to join the valve element and the armature, but provides less flow restriction.
Various features, advantages and the inventive aspects will be seen in the ensuing description and claims which are accompanied by drawings that disclose a presently preferred embodiment of the invention according to the best mode contemplated at the present time for carrying out the invention.